1. Field of the Invention
This invention pertains to asynchronous machines and, in particular, to asynchronous machines including a rotor of solid iron and a squirrel cage winding.
2. Description of the Prior Art
In starting a work-performing machine having a high power rating and a high nominal speed, such as, for example, blowers or compressors, use of the nominal starting voltage to asynchronously self-start the main drive motor of the machine may result in an excessively large voltage dip in the network voltage due to the large starting current required. Additionally, the motor may be subject to thermal overload. If, on the other hand, an attempt is made to reduce the nominal starting voltage to the point where the starting current and the voltage dip in the network voltage are permissible, the resultant starting torque may become insufficient to overcome the counter torque and, thus, to bring the machine into operation. It is, therefore, customary to provide such a machine with additional starting devices, such as, for example, starter motors coupled to the main machine or separate starting machine sets. These additional starting devices are expensive, however, and require additional servicing.
Non self-starting asynchronous machines used as generators ae also known wherein, for reasons of mechanical strength, the machines employ high speed solid rotors instead of laminated rotors. Thus, German Offenlegungsschrift No. 25 37 706, discloses such an asynchoronous machine wherein the machine has high power and speed and employs a squirrel cage winding arranged in its solid iron rotor. In this machine, the bars of the squirrel cage winding are arranged in slots which are open toward the outer surface of the rotor. The bars are further designed so that they also form a copper jacket surrounding the surface of the rotor.
It is an object of the present invention to provide an asynchronous machine which when used as a motor which is directly coupled to a high-speed, high power rated work-performing machine, is capable, during asynchronous self-star, of overcoming the countertorque of the latter machine safely without thermal overload and without excessive voltage dips occurring in the network voltage.